Some integrated circuits (ICs) and other devices have a large number of pins or contacts, which require an extended testing period and specialized test equipment to test the devices. Three tests commonly applied to devices are structural tests, parametric tests, and functional tests. Structural testing typically involves operating a built in self test (BIST) in the device. For example, structural testing may involve applying voltages to certain pins or conductors on the device and monitoring outputs that provide information as to whether the device is operating properly. Structural testing on a digital circuit may check all the gates to make sure they are operating correctly. Structural testing typically does not test all the pins of the device and is very time consuming. In some examples, a device with one-hundred pins may only require a few pins contacting the test station to complete the structural test, but the test may take as long as a minute to complete. Short circuits and open circuits on the remaining pins are not tested during structural testing.
Functional testing requires coupling between the test station and all the pins of the device. The functional testing may include tests for open circuits, short circuits, proper voltage levels, and other possible defects in the device. Unlike structural testing, functional testing does not run the BIST, but it typically performs tests on all the pins. A functional test may take one second for a one-hundred pin circuit whereas structural testing on the same device may take as long as one minute. Parametric testing is similar to functional testing in that it typically requires contact with all the pins of the device, but it tests ranges of the device. For example, it may test to assure that a current draw does not exceed a specific limit when a range of voltages is applied to a pin. Parametric testing takes longer than functional testing, but not as long as structural testing. In some examples, the one-hundred pin device described above may take two seconds to perform the parametric testing.
Conventional test equipment performs one of the three tests, structural, functional, or parametric. Accordingly, fully testing circuits requires the circuits to be connected and disconnected from different test equipment for each test. This connecting and disconnecting is time consuming and the requirement of different test equipment for each test is costly.